A carbon nanohorn is a material having a hollow cone-shaped structure in which a tip of a tube formed of a single layer of a graphene sheet is closed, i.e., a horn-shaped structure. In general, the carbon nanohorns can be obtained as spherical aggregates in each of which a number of carbon nanohorns are aggregated with the tips thereof facing outside (see, for example, Japanese Laid-Open Patent Application JP-P 2003-20215A). The carbon nanohorn has a diameter of approximately 2 to 5 nm, and the aggregate has a diameter of approximately 50 to 150 nm. The carbon nanohorn aggregate is characterized in that a surface thereof has a very irregular structure, and therefore expected to be applied as a catalyst support or gas absorbent.
Methods for manufacturing carbon nanohorns include a laser ablation method, an arc discharge method, and the like. Among them, the laser ablation method is a method in which a target made of carbon such as graphite is irradiated with a carbon dioxide gas laser in inert gas such as argon gas, and can manufacture relatively high purity carbon nanohorns (see, for example, Japanese Laid-Open Patent Application JP-P 2005-350275 A and JP-P 2005-350349 A).
Collection of manufactured products containing carbon nanohorns can be carried out by a method in which the products are deposited on an appropriate substrate for collection, a particulate collecting method by a dust bag, a method in which inert gas is circulated in a reaction container to collect the products by a flow of the inert gas, or the like (see, for example, Japanese Laid-Open Patent Application JP-P 2001-064004 (particularly, see paragraph [0018]).
The collection of the products containing carbon nanohorns may also be carried out with the use of a filter provided in an inert gas circulating path or the like connected to a reaction chamber (see, for example, Japanese Laid-Open Patent Application JP-P 2002-234715 A, and National publication of translated version of PCT Application JP-P2005-501789A. In addition, the products deposited onto an inner wall surface of the reaction chamber are collected by being scraped with a scraper (see, for example, Japanese Laid-Open Patent Application JP-P 2002-234715 A).